1. Field of the Invention
The present invention relates to instruments and devices for measuring temperature, and particularly to a gas-actuated thermometer containing an expandable gas volume therein that moves an indicator within the indicator tube as the temperature of the gas changes.
2. Description of the Related Art
The liquid-actuated thermometer, i.e., mercury filled, has been known for a considerable period of time. The use of the pure element mercury (Hg) in thermometers of various temperature ranges provides a number of advantages and conveniences. Pure mercury is a liquid at all ambient temperatures, from the hottest near-equatorial desert climates to winter polar temperatures. Mercury expands and contracts readily with temperature changes, thereby providing a ready indication of the temperature when the mercury is enclosed in an accurately marked tube or vial. Moreover, pure mercury is not particularly expensive to extract or refine, particularly in the relatively small amount required for the typical thermometer used to measure the ambient temperature or for medical use.
However, mercury is not without its problems and hazards. Historically, mercury was not recognized to be a hazardous or poisonous substance. More recently, however, mercury has been so recognized, particularly in its pure liquid form. While there is no hazard so long as the mercury remains completely enclosed in a hermetically sealed and unbroken container, the typical glass bulb and tube mercury thermometer is prone to breakage, and when such breakage occurs, the subsequent release of the mercury therein can prove extremely hazardous to individuals who might contact the released mercury, particularly if the thermometer is an oral thermometer that breaks in the mouth of the individual. The conventional construction of the mercury thermometer, which includes a metal bulb (for better heat transfer) that is bonded to a glass column or tube, is also somewhat prone to leakage between the metal and glass interface. Moreover, the conventional mercury thermometer is formed as a relatively small diameter tube having a nearly circular cross-section (with perhaps some slight widening of one face to act as a magnifier), in order to provide sufficient length in the tube to show the mercury expansion readily. This configuration leaves little room for the inclusion of two different temperature scales, i.e., Celsius and Fahrenheit.
As a result, various alternative temperature-measuring principles have been developed over the years. Purely electronic thermometers utilizing thermocouples have been developed relatively recently (in comparison to the well-known mercury thermometer), but earlier “hybrid” thermometers utilizing a combination of a liquid and a gas have also been developed in the past. Many, if not most, such thermometers use the expansion and contraction of a gas due to temperature change to drive a liquid in a tube that thereby indicates the temperature. In sonic cases, the liquid actuates a Bourdon tube to drive a rotating hand in a circular dial. The various devices of this type that depend upon the principle of the expansion and contraction of a gas and that are known to the inventor also use a liquid and/or a remotely located indicator that is not directly attached to or located with the temperature sensing bulb or element.
Thus, a gas-actuated thermometer solving the aforementioned problems is desired.